CN107148771B

CN107148771B - Method for transmitting data to a plurality of receiver devices, transmitter and receiver device

Info

Publication number: CN107148771B
Application number: CN201580061041.4A
Authority: CN
Inventors: A·阿尔·拉维; L·汉弗莱; 特雷弗·林尼; I·霍斯利
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 2014-09-30
Filing date: 2015-09-29
Publication date: 2020-10-23
Anticipated expiration: 2035-09-29
Also published as: EP3202130A1; CN107148771A; WO2016050765A1; US20170244446A1; EP3202130B1; US10193594B2

Abstract

A method, a transmitter and a receiver device for transmitting data to a plurality of receiver devices. A method of transmitting data from a sender device (16) to a plurality of receiver devices (51, 52), each of the plurality of receiver devices (51, 52) being connected to the sender device (16) via a respective line connection (21, 22), the method comprising the steps of: -sending a common signal onto all or both of said respective line connections (21, 22); and using a multiple access technique to enable generation of respective virtual data channels for transmitting data from the transmitter device (16) to each of the receiver devices (21, 22) via their respective virtual data channels.

Description

Method for transmitting data to a plurality of receiver devices, transmitter and receiver device

Technical Field

The present invention relates to a method and apparatus for transmitting and receiving a signal through a wire pair. Such methods include all of the various Digital Subscriber Line (DSL) methods specified in various International Telecommunications Union (ITU) standards and currently further developed in the ITU. Typically, each such pair of wires comprises a twisted metallic pair (typically copper) commonly found in telephone access networks around the world.

Background

DSL technology takes advantage of the fact that, while conventional twisted metal pairs, originally installed to provide only Plain Old Telephone Service (POTS) telephone connectivity, may only be intended to carry signals at frequencies up to a few kilohertz, in fact such lines may often reliably carry higher frequency signals. Furthermore, the shorter the line, the larger the frequency range over which signals can be reliably transmitted (particularly using techniques such as Discrete Multitone (DMT)). Thus, as access networks evolve, telecommunication network providers have expanded their fiber infrastructure outward to the edge of the access network, making the length of the last portion of each connection (which is still typically provided by a metal twisted wire pair) to the end user subscribers shorter and shorter, correspondingly resulting in greater bandwidth potential through the increasingly shorter twisted metal wire pair connections without having to incur the expense of installing a new fiber connection to each subscriber.

However, a problem with using high frequency signals is that where there is more than one metal pair carrying similar high frequency signals close to each other, a phenomenon known as crosstalk can cause significant interference to reduce the effectiveness of the line to carry high bandwidth signals. In short, a signal from one line can "leak" onto a nearby line carrying a similar signal and appear as noise to another line. Although crosstalk is a known problem even at relatively low frequencies, the magnitude of this effect tends to increase with frequency to the point where indirect coupling (e.g., from the near end of the second line to the far end of the first line) can be as great as direct coupling (e.g., from the near end of the first line to the far end of the first line) at frequencies in excess of several tens of megahertz (depending on the length of the line in question).

To mitigate the problems caused by crosstalk (particularly the well-known far-end crosstalk or "FEXT"), a technique called vectoring has been developed in which knowledge of the signals transmitted over the crosstalking lines is used to reduce the effects of crosstalk. Typically, a single DSLAM serves as a common generator for multiple downstream signals on multiple crosstalkers, and also serves as a common receiver for multiple upstream signals from the same multiple crosstalkers, where each of the lines terminates in a single Customer Premises Equipment (CPE) modem, making general processing impossible at the CPE end of the line. In this case, the downstream signal is pre-distorted to compensate for the expected effect of the crosstalk signal transmitted on the adjacent crosstalk line, so that at the reception of the CPE device, the received signal is similar to the signal that would be received if no crosstalk signal were transmitted on the crosstalk line. Upstream signals, on the other hand, are post-distorted (or detected in a manner equivalent to that in which they have been post-distorted) after being received at a common receiver (DSLAM) to take into account the effects of crosstalk that has leaked into the signal during their transmission.

This vectoring technique can handle cases where indirect coupling is significantly weaker than direct coupling with great success. However, vectoring is less effective because the relative strengths of direct and indirect couplings are close to each other.

WO 2008/005507 describes a system for performing adaptive multi-carrier code division multiple access (adaptive MC-CDMA or AMC-CDMA), which is particularly suitable for power line transmission systems transmitting data over lines intended to carry power. Such a system may have many devices connected to each other over a common transmission medium (power line), for which it is not possible to transmit signals from one transceiver to another over dedicated respective line pairs, as is the case for conventional telephone access networks. Such transmission media are subject to continuously changing conditions. Thus, the system AMC-CDMA is adapted to allow for fast variations in bit loading using the MC-CDMA modulation method.

US 2005/002441 describes a multi-carrier code division multiple access transmission technique for transmitting data over a VDSL link comprising a single twisted copper pair connection between two cooperating VDSL modems. A drawback to using CDMA is that the multiple chips required for each data bit to be transmitted are mitigated by simultaneously transmitting multiple chips (chips) associated with different data bits. For this reason, the inventors refer to its scheme as multicode multicarrier code division multiple access (or MC-CDMA). The signal transmitted through other adjacent lines results in FEXT which is considered noise because it is independent of the signal transmitted through the line connecting the cooperating MCMC-CDMA modems.

"Multiple users adaptive modulation schemes for MC-CDMA" [ published in Global communications Conference,2004, GLOBECOM' 04, IEEE DALLAS, TX, USA 29 Nov-3 Dec 2004, Picataway, NJ, USA pages 3823 3827XP010758452, ISBN: 978-0-7803-. This subject matter is studied herein and a configuration is proposed that not only allows multiple users to employ adaptive modulation, but also results in an equivalent subcarrier concept that allows a set of subcarriers to be represented by the equivalent subcarriers of a conventional OFDM modem, allowing various powerful bit/power loading schemes originally developed for OFDM to be deployed directly to MC-CDMA.

WO2013026479 by the ericsson application proposes a method of transmitting signals in such a case (i.e. where indirect coupling is comparable to direct coupling for a given line), which involves transmitting signals intended for reception by a single CPE device (a first CPE device) onto the line directly coupled to the first CPE device and only indirectly onto the crosstalk line coupled to the first CPE device (which is directly coupled to a second CPE device). Using a Time Division Multiplexing (TDM) approach enables data to be sent (in different time slots) to two respective CPE devices (where the data is sent over two lines at a time to only one of the CPE devices at a time). To ensure that the two signals constructively interfere at the receiving CPE device, the same signal transmitted over one line is pre-distorted (e.g., to introduce delay and/or phase variation) before being transmitted over the other line to account for variations in the direct coupling path relative to the indirect coupling path.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a method of transmitting data from a transmitter device to a plurality of receiver devices, each of the receiver devices being connected to the transmitter device via a respective twisted metal wire pair, the method comprising the steps of: transmitting a common signal onto all or both of the respective pairs of lines; and enabling generation of respective virtual data channels using a multiple access technique to transmit data from the transmitter device to each of the receiver devices via their respective virtual data channels.

In this manner, the set of twisted metal wire pairs becomes a "common" shared channel over which a plurality of virtual channels are superimposed (i.e., virtual channels are superimposed over underlying common shared channels). However, it is interesting to observe that this "common" shared channel consists of multiple different sub-channels grouped together at each receiver device (e.g., a single direct path channel connecting a transmitter directly to a respective receiver by a twisted metal pair, and one or more indirect crosstalk paths from the transmitter to the receiver via at least one twisted metal pair connected between the transmitter and another one of the receivers). Thus, a "common" shared channel is referred to hereinafter as a composite channel comprising a combination of direct-path subchannels and indirect-path subchannels.

This aspect of the present invention is distinguished from prior art related to the use of MC-CDMA techniques in an environment where the physical environment of the channel used to transmit data is essentially a shared physical channel (i.e., no spatial diversity), such as WO 2008/005507, which relates to a power line system where the channel is formed by subscriber premises power cabling, US 2005/002441, which relates to a single twisted copper pair connection between two modems, and the aforementioned MC-CDMA paper of Tang C et al, where the channel is an over-the-air wireless channel in that it is used in an environment where each of the single transmitter devices is connected to multiple receiver devices via respective twisted metal pair connections/channels. The present inventors have realised that due to the effects of crosstalk, particularly at higher frequencies, the cost (in terms of power and hence bandwidth consumed in combating crosstalk effects (e.g. by vectoring)) of trying to maintain the independence of the channels to continue to utilise them as independent isolated channels becomes too high at higher frequencies, and so a better solution is to treat the individual channels as a single composite channel. In this regard, then, one point that must be considered is how to best utilize a single common composite channel formed by a plurality of spatially diverse twisted copper pair connections each of which is connected to a respective receiver, and the solution of the first aspect of the present invention is to send a common signal to all of the plurality of twisted metal pair connections and to use a multiple access technique such as MC-CDMA to enable different data to be sent to different receivers.

The composite channel will (typically) be different at each receiver, since the individual sub-channels from the transmitter to each respective receiver will (typically) be different at each receiver, and in addition, the manner in which the sub-channels are combined (where some sub-channels tend to constructively interfere with each other and others tend to destructively interfere with each other) will also be different from receiver to receiver. Furthermore, the composite channel for each receiver will additionally vary with frequency, and the variation in frequency will (typically) also differ from receiver to receiver. In this way, the composite channel may be "good" for one receiver at one frequency and "bad" for another receiver at the same frequency. The quality of the composite channel may also vary over time, however, such variation over time tends to be less important for channels formed on paths formed by twisted metal pairs than channels formed by wireless channels, and thus such variation over time is largely ignored for purposes of the present invention. In some preferred embodiments, new measurements of the composite channel are taken from time to time, and the multiple access configuration is reconfigured only if the (new) measurements indicate that significant improvement will result from such reconfiguration (because the composite channel has changed significantly enough from performing the last reconfiguration).

Preferably, the common signal is a discrete multi-tone signal, wherein the modulation level of each tone may be varied. Furthermore, it is further preferred that different modulation levels are used for data sent within a common signal within a given tone to different receiver devices, depending on the difference in received signal-to-noise ratio of the signals received at the different receiver devices for the given tone. For example, if a first receiver determines that a DMT signal should be successfully detected with sufficient accuracy to allow x bits of data to be reliably received in a particular tone, while a second receiver determines that the same DMT signal should be successfully detected with sufficient accuracy to allow y bits of data (per frame) to be reliably received in that tone, where y is not equal to x, it is preferable if the transmitter can combine the data in the following manner: the amount of data transmitted to the first receiver depends on x and the amount of data transmitted to the second receiver depends on y by using a modulation technique that modulates the data of the first receiver with a modulation level that depends on x and modulates the data to be transmitted to the second receiver using a modulation technique that modulates the data to be transmitted to the second receiver with a modulation level that depends on y. For example, modulation may involve selecting a constellation point from within a modulation constellation, and the modulation level may correspond to the number of different constellation points within the modulation constellation (or more specifically, to the base 2 logarithm thereof). With the TDMA approach, this simply requires selection from different modulation constellations according to the time slot, and similarly for FDMA where different tones are allocated to different receivers, it requires selection from a modulation constellation that is appropriate for the receiver to which the tone has been allocated. In the case of the CDMA method, data of different receivers is modulated using an appropriate modulation constellation for each receiver and each tone, and then the modulation values are combined into a plurality of chips to be transmitted on the respective tones using different spreading codes for the different receivers.

Since the quality of the composite channel varies at different frequencies for different receivers, it may be advantageous in some cases to use Frequency Division Multiple Access (FDMA), although in general any type of multiple access technique may be used (e.g., a Time Division Multiple Access (TDMA) technique may be employed in which the time at which a common signal is transmitted and/or received is used to associate the signal with one of a plurality of predetermined time slots-this may be repeated periodically with a periodicity associated with a "frame" comprising the plurality of time slots-and the data carried in the signal within a particular time slot may be associated with a particular receiver according to a predetermined allocation of time slots to the receiver). The reason for the advantage of FDMA (compared to (over) say TDMA) is that variations in the composite channel quality with both frequency and receiver can be exploited.

For example, if in a simple example chosen for illustrative purposes, the system includes a single transmitter (e.g., AN Access Node (AN) such as a Digital Subscriber Line Access Multiplexer (DSLAM)) and two receivers a and B (e.g., DSL or g.fast modems), each connected to the transmitter over a single twisted metal pair connection, and wherein the transmitter transmits a common signal to both twisted metal pairs using Orthogonal Frequency Division Modulation (OFDM) or discrete multi-tone (DMT) modulation schemes, if a determines based on channel measurements that a particular tone X can support 4 bits per symbol, while a second tone Y can only support 2 bits per symbol, while B determines that tone X can only support 2 bits per symbol and tone Y can support 4 bits per symbol, then the data that can be transmitted over tone X is designated as being specific to receiver a, while the data transmitted over tone Y may be designated as being dedicated to receiver B. In this way, both a and B will receive data at 4 bits per symbol for tone X and Y combinations, while if TDMA is used, the best effect that can be achieved with a 50% duty cycle for each receiver (i.e., one symbol for receiver a, followed by one symbol for receiver B, etc.) will be 6/2-3 bits per symbol for tone X and Y combinations (assuming that the complexity of changing modulation from one symbol to another can be handled by the AN).

CDMA techniques may also be useful, particularly when the quality of the channel varies over time at different tones. In such an environment, it must generally be fairly conservative in terms of how many bits per symbol and per tone the system attempts to transmit. Using multi-carrier CDMA (MC _ CDMA), the signal can be effectively spread over multiple different tones and if the quality of one tone deteriorates, but is compensated for by increasing the quality of another tone, the average overall quality provided remains constant and communication is unaffected. The embodiments described below explain in more detail how MC-CDMA is used.

For the reasons stated above, Frequency Division Multiple Access (FDMA) techniques or Code Division Multiple Access (CDMA) techniques are preferably used, although any multiple access technique may be employed.

When FDMA techniques are used, it is advantageous to employ smart tone allocation techniques that allocate tones to receivers in a manner that attempts to maximize both the overall data rate and the data rate of the receiver that achieves the worst data rate. An example of one such smart tone allocation technique is described in more detail below with reference to specific embodiments.

Note that in embodiments of the present invention, the method of the first aspect of the present invention (hereinafter referred to as "combined direct and indirect channel mode" or "combined channel mode" or "CCM") is employed only in a predetermined (preferably, upper) portion of the available spectrum that is available for communication over a wire-pair connection. Preferably, this is done by allocating certain tones to operate in CCM mode, while other tones operate in another mode of operation, such as vectored DMT. Preferably, CCM is employed only in a predetermined upper part of the spectrum above the cutoff frequency (hereinafter "CCM cutoff frequency"), and in the lower part of the available spectrum below the cutoff frequency, an alternative mode such as vectored DMT is used. Note also that in some embodiments, CCM is only used to transmit data in the "downstream" direction (i.e., from a single transmitter to multiple receivers); in such an embodiment, the upstream signal is only transmitted in frequencies below the CCM cutoff frequency. Preferably, dynamic and flexible techniques are employed to determine the CCM cutoff frequency to be used. It can be reasonably assumed that (in general) vectoring techniques work well to the extent that crosstalk coupling starts to become almost (about) as large a frequency range as direct coupling, but then increasingly larger frequencies become less and less efficient (in terms of spectral efficiency for a given transmission power level). However, the spectral efficiency of a Combined Channel Mode (CCM) arrangement does not decrease as rapidly at higher frequencies. Preferably, the technique involves measuring channel quality at different frequencies, and wherein training signals are transmitted over different twisted metal pairs so that an assessment of various crosstalk couplings can be assessed, and wherein the selection of the CCM cutoff frequency is made based on these measurements in a manner that seeks to maximize the overall spectral efficiency of a system using vectored DSL below and CCM above the CCM cutoff frequency. In some embodiments, this may be achieved by selecting as the CCM cutoff frequency or cutoff tone a frequency (or tone) at which all tones having frequencies above the cutoff frequency (or frequencies above the cutoff tone) are evaluated as being able to carry less than a predetermined number of bits when operating in vectored DMT mode (or tones above which more than a predetermined proportion of the frequency is evaluated as being able to carry less than a predetermined number of tones, or an average (or other average) number of bits per tone evaluated above that frequency is below some predetermined number of frequencies, etc.).

Other aspects of the invention relate to apparatus that performs the method, particularly in the form of modems, such as end user modems and Access Nodes (ANs), such as Digital Subscriber Line Access Multiplexers (DSLAMs), particularly such modems that are operable to communicate in accordance with the g.fast protocol and that are deployable across a short twisted metal pair (or group of pairs) extending between a downtake and a customer premises such that the twisted metal pair has a length of less than 500 meters, and most preferably about 250 meters or less. Another aspect relates to processor-executable instructions for causing a modem or modems to perform the method of the first aspect of the invention; similarly, another aspect relates to a carrier medium (in particular a non-transitory carrier medium such as an optical or magnetic storage device (such as a floppy disk, hard drive, CD or DVD) or a solid state storage device such as an SSD drive or a USB thumb drive).

Accordingly, a second aspect of the present invention relates to a transmitter for transmitting data to at least a first and a second receiver device via respective first and second line connections directly connecting each respective receiver device to the transmitter device using a discrete multi-tone communication method employed at frequencies where there is significant indirect coupling between the line connections, the transmitter device comprising: a data combiner for combining a first set of data to be transmitted to the first receiver and a second set of data to be transmitted to a second receiver into a single common discrete multi-tone signal; and a line driver for driving the first line connection and the second line connection with a common signal.

A third aspect relates to a receiver device for receiving data transmitted to the receiver device over a wire connection from a transmitter according to the second aspect, the receiver comprising: a receiver for receiving a common discrete multi-tone signal; and a data extractor for extracting from the common signal a first set of data transmitted by the transmitter for reception at the receiver device. In some preferred embodiments, the data extractor includes a despreader module for despreading the received signal in accordance with a code division multiple access technique. In an alternative preferred embodiment, the data extractor comprises a tone selector for selecting a subset of values detected by the receiver and associated with different tones based on a predetermined allocation of tones assigned by the transmitter to the receiver.

Drawings

In order that the invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 is a schematic diagram illustrating an example broadband connection deployment of a Distribution Point Unit (DPU) and two customer premises having associated Customer Premises Equipment (CPE) modems connected to the DPU via respective Twisted Metal Pair (TMP) connections;

fig. 2 is a schematic block diagram illustrating the major components in a modem-to-modem connection operating in accordance with a first embodiment of the present invention;

fig. 3 is a schematic block diagram similar to fig. 2 illustrating the major components in a modem-to-modem connection operating in accordance with a second embodiment of the present invention;

FIG. 4 is a flowchart illustrating control steps performed by the controller unit in FIG. 3;

fig. 5 is a schematic block diagram similar to fig. 2 and 3 illustrating the major components in a modem-to-modem connection operating in accordance with a third embodiment of the present invention; and

fig. 6 is a flowchart illustrating control steps performed by the controller unit in fig. 5.

Detailed Description

FIG. 1 illustrates generally an example broadband deployment in which embodiments of the present invention may be employed. As shown in fig. 1, AN example deployment includes a Distribution Point Unit (DPU)10, the DPU10 being connected to two customer premises 31, 32 (which in this example are apartments within a single premises 30) via respective Twisted Metal Pair (TMP)

connections

21, 22, the

TMP connections

21, 22 being connected between AN Access Node (AN)16 (e.g., a Digital Subscriber Line Access Multiplexer (DSLAM)) within the DPU10 and respective Customer Premises Equipment (CPE) modems 51, 52 within the

respective customer premises

31, 32 via respective network termination points 41, 42 within the

respective customer premises

31, 32. The DPU10 further comprises: an Optical Network Terminal (ONT) device 14 providing a backhaul connection from the DPU10 to a local exchange office building via a fiber optic connection, such as a Passive Optical Network (PON); and a controller 12, the controller 12 coordinating communications between the AN16 and the ONTs 14 and may perform some management functions, such as communicating with a remote Persistent Management Agent (PMA).

It will be apparent to those skilled in the art that the illustrated deployment involving a fiber backhaul connection from a distribution point and a twisted metal pair connection from the distribution point to a customer premises is just such a deployment for which the g.fast standard is intended to be applicable. In this case, the TMP connection may be as short as a few hundred meters or less (e.g. perhaps only a few tens of meters) and so very high frequency signals (e.g. up to a few hundred megahertz) may be used to communicate through the short TMP because the attenuation of the high frequency signals is insufficient to prevent them from carrying useful information due to the short lines. However, crosstalk becomes an important issue at such high frequencies. This obviously would be the case in particular, where the crosstalking lines run alongside one another over part of their length (as in the case illustrated in fig. 1); however, crosstalk is still a problem at high frequencies (e.g., in excess of 80MHz), even where the lines are close to each other for only a very small portion of their total length (e.g., only when leaving the DPU 10). Fast currently proposes to simply use vectoring techniques at all frequencies where there are crosstalk lines to mitigate the effects of crosstalk. However, embodiments of the present invention use alternative techniques to mitigate the effects of crosstalk.

First embodiment

Referring now to fig. 2, there is shown a schematic illustration of the main components within the AN16 and

CPE modems

51, 52 according to a first simple embodiment chosen to illustrate the basic principles of the method, allowing the use of indirect channels associated with crosstalk effects, rather than simply mitigating by employing vectoring techniques.

As shown, AN16 according to the embodiment illustrated in fig. 2 includes first and second data sources, data encoder and serial to parallel converter (DSDESP)

modules

1611 and 1612. These are basically conventional functions in DSL modems and are used herein except to note that the output is a set of data values d₁-d_MEach data value may be mapped to both a set of one or more bits and to a point within a modulation signal constellation associated with the respective tone on which the data value is to be transmitted, as will not be described further. For example, if pitch t is determined₁Capable of carrying 3 bits of data, the corresponding data value will be set to 2³One of 8 different values (e.g., set to a decimal number between 0 and 7), each of which corresponds to a different constellation point within an associated signal constellation having 8 different constellation points. The data values of a single symbol may be considered to form a vector of data values (one for each data-carrying tone) and together carry user data to be transmitted to the end users associated with the respective end user modems 51, 52, along with any overhead data (e.g., forward error correction data, etc.).

Also noteThat is, since the present embodiment employs Code Division Multiple Access (CDMA), each

DSDESP module

1611, 1612 generates a data value for each tone, such that both

modules

1611, 1612 generate data values (e.g., d) for transmission over tone 1₁ ¹And d₁ ²). These data values do not necessarily relate to the same number of bits as will be explained in more detail below. For example, it is possible that modem 51 may determine that tone 1 can support 3 bits per symbol, while modem 52 may determine that tone 1 can only support 2 bits per symbol. In this case, DSDESP 1611 may generate a 3-bit data value (e.g., a number between 0 and 7), d₁ ¹And DSDESP 1612 may generate 2-bit data values (e.g., numbers between 0 and 3).

The data values leaving each

DSDESP block

1611, 1612 are then passed (in appropriate order) to a respective multi-bit level quadrature amplitude modulation (M-QAM)

modulator

1621, 1622, which converts each input data value into a respective complex number x₁ ¹To x_M ¹And x₁ ²To x_M ²Each complex number represents a complex point within a complex constellation diagram. For example, the digital value d₁ ¹The complex number 1-i of tone 1 may be mapped by M-QAM modulator 1621 to 7(═ 111), where tone 1 has been determined (by modem 51) to be each capable of carrying 3 bits of data.

Then, these complex numbers x₁ ¹To x_M ¹And x₁ ²To x_M ²Each of which is input to a spreader module 1630 (which in this embodiment is a single common spreader module 1630), the spreader module 1630 performs conventional CDMA spreading operations given by the equation:

to generate a set of "chips"

So that k are plural

(for all i from i-1 to i-k) is converted to P chips

(for all P from P-1 to P-P), where P is the length of the spreading code used and k is the number of different data streams multiplexed using the CDMA technique employed. For all M groups K

The combining and spreading is performed (for all M from M-1 to M-and all i from i-1 to i-k) to generate respective M groups of P combined and spread chips

(for all M from M-1 to M-M, and for all P from P-1 to P-P). In this embodiment, there are 2 such data streams (one for each end user modem 51, 52) such that k is 2 and the length of the spreading code used is 2 such that P is 2 (hence M sets of complex pairs)

And

is converted into M sets of chip pairs

And

). In the present embodiment, M sets of chip pairs are used

And

transmitted as 2 frames, each frame contains M chips, such that the original complex number is spread out over time, where the M chips are transmitted over corresponding M tones in a conventional discrete multi-tone (DMT) fashion.

It will be appreciated that the effect of combining and spreading is to combine data for different end user modems together and then spread it out again so that it can be later recovered by performing a despreading action. In this manner, a virtual data channel is generated whereby although virtually all of the same data is actually sent through both

TMPs

21, 22 to both

modems

51, 52, data destined for the first modem 51 is sent through the first virtual data channel from the first data source, encoder and S/P module 1611 to the first modem 51, and data destined for the second modem 52 is sent through the second virtual data channel from the second data source, encoder and S/P module 1612 to the second modem 52. The well-known CDMA principles to achieve this can be easily demonstrated using a simple numerical example (ignoring the effects of noise that is temporarily imparted to the transmitted signal during transmission over the channel), and therefore:

in the present embodiment, the following spreading codes {1, 1} and {1, -1} are considered to be used; in other words,

also consider that for a single tone (tone 1), we have the complex value 1+ i sent to the modem

And causing the complex value-i to be sent to the modem

After combining and spreading, they are converted into two chips

And

the two chips are then transmitted in two separate frames (via IFFT modeling the front-end channel, etc., as will be discussed briefly below), and once they have been received, a despreading operation is performed in the

modems

51, 52, with the modem 51 using the spreading code {1, 1} and the modem 52 using the spreading code {1, -1} to use

To recover the data, wherein the data is made available in the modem 51 when m-i-1 (the first tone is used for the first receiver-modem 51)

(or after appropriate normalization)

) And in the modem 52 when m 1, i 2 (the first tone for the second receiver, modem 52)

(or after appropriate normalization)

)。

Once the chips are generated in the manner described above, the remaining processing is conventional and not relevant to the present invention. Thus, in an Orthogonal Frequency Division Multiplexing (OFDM)/DMT system, the appropriately generated chips are passed from spreader module 1630 to Inverse Fast Fourier Transform (IFFT) module 1640 for converting the multiple chips for a single frame into a combined orthogonal time domain signal in the normal manner. The time domain signal is then processed again by a suitable Analog Front End (AFE) module 1650 in any suitable such manner, including any normal conventional manner. Incidentally, in the present embodiment, only a single AFE module 1650 is used, but of course two different AFE modules, one for each TMP21, 22; note that in embodiments where the common signal to be transmitted over multiple TMP connections is processed by a single common AFE (as in the present embodiment), the resulting advantage is that the resulting signals sent onto the individual TMP connections will tend to be more similar than when they have been pre-processed by the individual AFE modules (due to the inevitable small differences in the analogue components that make up the AFE modules). In any case, in this embodiment, after processing by the AFE module 1650, the resulting analog signals are jointly transmitted onto the two

TMP connections

21, 22 via a coupler device 2000, which coupler device 2000 simply couples the two

TMP connections

21, 22 to the common AFE module 1650.

During transmission through the

TMP connection

21, 22 the signal will be modified in the normal way according to the channel response of the channel and due to external noise impinging on the connection. Specifically, there will be crosstalk (and most particularly far-end crosstalk) between the two direct channels (the direct channel being one from transmitter 16 to modem 51 via TMP21 and one from transmitter 16 to modem 52 via TMP 22) resulting in reception of signals at

modems

51 and 52 from the indirect channels (e.g., signals sent onto TMP21 but received at modem 52 and signals sent onto TMP22 but received at modem 51). However, since the same common signal is sent on both TMP connections, the net effect at each receiver/

modem

51, 52 is that of a single combined (direct and indirect) channel and can be evaluated and considered by the receiver/modems 51, 52 in the normal way as if there were no crosstalk interference. In practice, in general, the indirect receive component of the (combined direct and indirect) receive signal may increase the SNR of the receive signal for a given

modem

51, 52 compared to the case where there is no indirectly received signal component (i.e., no signal is sent on the

direct channel

22, 21 of the other modem 52, 51) and only a single direct signal is sent on the directly connected TMP21, 22.

After passing through the

TMP connection

21, 22, the signal is received at an Analog Front End (AFE) module 5150, 5250 (by both modems 51, 52), which

AFE module

5150, 5250 performs the usual analog front end processing. The signals thus processed are then passed to a Fast Fourier Transform (FFT)

module

5140, 5240, which

FFT module

5140, 5240 performs the usual transformation of the received signal from the time domain to the frequency domain. The signals leaving the

FFT modules

5140, 5240 are then passed to frequency domain equalizer (FEQ)

modules

5160, 5260 in this embodiment. The operation of such frequency domain equalizer modules is well known in the art and, therefore, will not be described further herein. It should be noted, however, that any type of equalization may be performed herein (such as using a simple time-domain linear equalizer, a decision feedback equalizer, etc.). For more information on equalization in OFDM systems, the reader is referred to: "Zero-Foring Frequency-Domain Equalization for Generalized DMTTranscript devices with Insufficient Guard Interval" by Tanja Karp, SteffenTrautmann, Norbert J. Fliege, EURASIP Journal on Applied Signal Processing 2004:10,1446 and 1459.

Once the received signal has passed through the AFE, FFT and FEQ modules, the resulting signal y will have the effect of some degree of error and external noise impinging on the line during transmission of the signal between the AN and modems 51, 52 due to incomplete equalization of the channel₁ ¹To

And t₁ ²To

It should be similar to the chips presented to the IFFT block in AN16

The error typically varies from receiving modem to receiving modem. This can be expressed mathematically as

And

wherein the content of the first and second substances,

is a value generated by a combined process of the signal received at the modem 51 through the AFE 5150, the FFT 5140, and the FEQ 5160

And code sheet

And not necessarily equal to the corresponding error of the second modem 52

These received values y for the modem 51 are then₁ ¹To

And the received value y for the modem 52₁ ²To

Are passed to their

respective despreading modules

5130 and 5230, where the

despreading modules

5130 and 5230 perform despreading operations. In the despreading operation, each modem uses its own spreading code to recover data destined for itself. In the present embodiment, the transmit chips are spread in time, so that despreading needs to be performed using a plurality of received signals received in different frames. Thus, in this embodiment, each

despreading module

5130, 5230 buffers the received value y₁ ¹To

And y₁ ²To

Until it has beenSufficient values are received to enable the despreading operation to be described mathematically by:

wherein, in

I indicates which receiving modem is performing the despreading operation (because different modems use different spreading codes) and p indicates which chips (within the sequence of chips that need to be reconstructed together to the desired complex value for detection by the M-QAM demodulator modules 5120, 5220) are related to the value (where in this embodiment different chips have been transmitted at different times-i.e., within different frames). In this embodiment, each complex value x is spread to two chips using a spreading code of length 2 and transmitted in adjacent frames such that after a pair of frames is received, two received and processed values for each tone m

And

multiplied by their respective spreading code values (i.e.,

and

) And then added together. Then, the obtained despread signal is subjected to

To

And

to

Passed to each respective M-

QAM demodulator module

5120, 5220, where each value is based on its value

Selecting the corresponding constellation point (e.g., by selecting the nearest free value

Constellation points of the represented points, unless trellis coding is used, etc.). The obtained data value

To

And

to

Should substantially (except for some small number of incorrect detection values caused by errors) correspond to the data values d of the corresponding M-

QAM

1621, 1622 originally input into the AN/transmitter 16₁ ¹To d_M ¹And d₁ ²To d_M ²And (7) corresponding. These values are then input into the corresponding decoder (and received data processing) module 5110, which decoder module 5110 reassembles the detected data and performs any necessary forward error correction, etc., and then presents the recovered user data to any service it addresses in the normal manner, thereby completing the successful transmission of the data.

Variations of the first embodiment

In the above embodiment, there are only two TMP connections between AN16 and the corresponding pair of end user modems. However, it should be understood that this scheme can be applied to any number of TMPs and corresponding modems by simply expanding the number of data sources, encoders and sets of S/P1611, 1621 and M-

QAM modulators

1621, 1622 modules, which feed expander module 1630 accordingly; furthermore, as will be apparent to those skilled in the art, it is of course necessary to increase the number of orthogonal spreading codes employed accordingly to be able to combine different sets of data together in a spreading operation, as well as to increase the number of sets of frames that need to be buffered before despreading is performed at a modem or the like.

It will be apparent to the skilled reader that the above-described CCM scheme may be considered as a type of multi-carrier code division multiple access (MC-CDMA) technique. It is therefore apparent that "chips" have been generated, which may be spread in time (as in the first embodiment described above) or frequency. To spread the chips in frequency, instead of generating one chip per tone in each frame, fewer data values d are generated per user/modem relative to the number of available tones₁ ¹To d_M ¹The group (2). For example, in the case of two users using a spreading code of 2 (as described earlier) (and assuming that all tones can carry the same number of bits per tone, unlike in the first embodiment), half the number of data values may be generated for each user as there are tones available to carry data values. Once the chips (two for each data value) have been formed, there will be exactly the same number of chips for carrying as the tones on which they are carried, and each chip is allocated to one tone. Since all chips are carried in one frame, there is no need in such an arrangement that the received chips are buffered before despreading, and thus the delay is reduced in such an arrangement.

On the other hand, it is desirable to ensure as much as possible that the same number of bits of tones can be carried (from the perspective of all receiving modems (although the actual number of bits that two tones can carry need not be the same for different modems, i.e., if modem 1 determines that tones 1 and 11 can each carry 3 bits, and modem 2 determines that tones 1 and 11 can each carry 2 bits, they will be good candidates for carrying two chips associated with the same data vector).

If it is necessary to use two tones which (for at least one receiving modem) are not equal in the estimated number of bits they can carry, some decision must be made as to what level of modulation to perform. However, it may be possible in some cases, for example, where even a given first tone can only reliably carry the hypothesis (say)2 bits under a conventional DMT scheme, the gain achieved using the CDMA method may enable the hypothesis 3 bits to be reliably carried over the combination of the given first tone when cooperating with a given second tone (particularly where the given second tone will be able to reliably carry 3 or more bits of data over the conventional DMT method).

Second embodiment

It will be appreciated that the above described embodiment with reference to figure 2 demonstrates the combined direct and indirect channel transmission method in a rather crude form to illustrate the basic principle. Turning now to fig. 3, a more complex implementation is described in which more than one transmission mode is used to enable greater spectral efficiency than can be achieved with the implementation illustrated in fig. 1 and described above.

Thus, in fig. 3, where the same reference numerals have been used for the same components, it can be seen that the extender module 1630 of fig. 2 has been replaced with an extender/vectoring module 1670, which extender/vectoring module 1670 performs conventional vectoring with respect to some tones and extension with respect to the remaining tones in a manner discussed in more detail below. It can be seen that additional changes from the embodiment of fig. 2 are included in this embodiment, a pair of

separate IFFT modules

1641 and 1642 replace the common IFFT module 1640 of the embodiment illustrated in fig. 2, and similarly separate Analog Front End (AFE)

modules

1651 and 1652 replace the common AFE module 1650 of fig. 2. Additionally, in the embodiment of fig. 3, because each

AFE

1651, 1652 is directly connected only to its associated TMP21, 22, no coupler module 1660 is required.Shown instead in fig. 3 is a block indicating that the effect of the

TMPs

21, 22 is to generate a (combined direct and indirect) channel response h for the TMP21¹(t)＝(h₁ ¹(t) h₂ ¹(t)) and h for TMP22²(t)＝(h₁ ²(t) h₂ ²(t)) -a combined matrix channel response which can be mathematically considered as a single one

Also explicitly shown in fig. 3 are

various controllers

1690, 5190 and 5290 located within the AN16, the first modem 51 and the second modem 52, respectively. As indicated by the dashed connecting lines in fig. 3, these controllers are able to communicate with each other (e.g., via a conventional Embedded Operations Channel (EOC), as is well known in DSL technology). The main function of the controller illustrated in this embodiment is to enable the AN16 on the one hand and the

modems

51, 52 on the other hand to cooperate in determining and setting the CCM cutoff frequency (discussed below) and in controlling the transmission of training signals to enable correct channel estimation to be performed, as will be described in more detail below with reference to fig. 4.

As can be seen from fig. 3, 4 sets of values are output from the extender/vectoring module (although in practice two of these sets are identical). Thus, the largest set of values output is from c₁To c_mThen outputs a set of predistorted complex numbers x'_M+1 ¹To x'_N ¹Then outputs the chip c₁To c_mAnd finally outputs a second, different set of predistorted complex numbers x'_M+1 ²To x'_N ². Note also that the first two sets of output values (c)₁To c_mAnd x'_M+1 ¹To x'_N ¹) Is passed to a first IFFT module 1641 and a second two sets of values (c)₁To c_mAnd x'_M+1 ²To x'_N ²) Is passed to a second IFFT module 1642.

Code sheet c₁To c_mIn accordance with the above referenceGenerated in the same manner as the first embodiment described in FIG. 2, and a complex value of x'_M+1 ¹To x'_N ¹By using conventional vectorization techniques by using the value x output by M-QAM block 1621_M+1 ¹To x_N ¹Predistortion generation to account for (in for x ') in the normal way done in accordance with well-known vectoring techniques based on estimated knowledge of the degree of crosstalk coupling from TMP22 to TMP 21'_M+1 ²To x'_N ²After its own predistortion) of the signal x to be transmitted onto the TMP22_M+1 ²To x_N ²The influence of (c). Extender/vectorization module 1670 lets value x_M+1 ²To x_N ²Predistorted to form an output value x 'in a similar manner'_M+1 ²To x'_N ²。

At each of the receivers, the received signal is processed in the normal manner by the AFE, FFT and FEQ modules to generate the values y on tones 1 to M, respectively, in the first modem 51₁ ¹To

And on tones M +1 through N

To

In the present embodiment, only the value

To

Is passed to a despreading module 5130 and the value

To

Is directly passed to the M-QAM demodulator module 5130. Thus, it can be seen that in this embodiment, essentially two different "channels" are used, where tones 1 to M are used for CCM mode, while tones M +1 to N are being used in conventional vectored DSL mode (note that these may also use modes according to the currently proposed g.fast draft standard which employs vectored DMT in a time-division multiplexed fashion, etc.). It is noted that if (as in the present embodiment) the chips are spread over time such that two (or more) frames are received and buffered before all chips needed to perform despreading actions to recover the transmitted user data are available, then according to the first embodiment the AN16 is required to schedule data transmitted at half (or less) the rate at which data transmitted over the vectored DMT mode channel is scheduled for transmission for the CCM mode. In this embodiment, this is handled by the data source, encoder, and S/

P modules

1611, 1612.

It is further noted that the procedure for performing channel estimation required for these two modes of operation (vectored DMT and CCM modes) needs to be performed slightly differently for the two modes. Thus, in this embodiment, the

controllers

1690, 5190 and 5290 cooperate in the manner described below with reference to fig. 4 to determine a cut-off frequency that will determine which tones to employ in CCM mode by specifying a value of M such that tones 1 through M are used in CCM mode and tones M +1 through N are used in vectored DMT mode (or similar), where 1 is the highest frequency tone available to the system and N is the lowest frequency tone available to the system. In addition, the controller controls the operation of the modem to perform the necessary channel estimation required to operate tones 1 through M in CCM mode.

Before turning to fig. 4, it is also worth mentioning that although the figures do not illustrate the components (from the

modems

51, 52 to the AN 16) necessary for performing the upstream transmission, it goes without saying that these components are included and have not been simply illustrated, since they are not relevant to the present embodiment. It should be noted, however, that upstream transmissions can be handled either by means of frequency division multiplexing according to DMT techniques according to the VDSL standard or using TDM methods according to the current draft version of the evolved g.fast standard.

Turning now to fig. 4, a method performed by the controller for coordinating transmissions between the AN and the

modems

21, 22 to use CCM mode for only a portion of the available tones will now be described. The method starts at step s10, in which method the modem performs a conventional synchronization, except that although the EOC channel is established (preferably using only low frequency tones), the SHOWTIME mode is not entered immediately upon completion of the conventional synchronization. The normal synchronization procedure includes performing channel estimation and evaluation of indirect coupling, etc., to be able to estimate appropriate vectoring parameters, etc. Upon completion of this step, AN EOC channel is established to enable the AN controller 1690 to communicate with the

modem controllers

5190, 5290. The method then proceeds to step s20, where the AN controller 1690 determines AN appropriate CCM cutoff frequency. In this embodiment, this is achieved by estimating the lowest tone which has been estimated to be able to carry (by both modems 51, 52) no more than 1 bit and for which the average (average) estimated number of bits per tone for all tones below it is greater than two bits per tone and the average (average) estimated number of bits per tone for the remaining tones (both itself and all tones having a higher frequency than itself) is less than two bits per tone, or marking the first 20% of all available tones (i.e., where M is N/5) such that the tones where the CCM tone changes from tone 1 to tone M N/5 are selected as the CCM cutoff tone, whichever of these two options has the highest number (i.e., has a lower frequency to maximize the number of tones allocated to the CCM mode, since the tones are numbered from 1 (highest frequency) to N (lowest frequency)).

Having selected the CCM cutoff frequency/cutoff tone, the method proceeds to step S30, and in step S30, a common training signal is generated and transmitted in the CCM mode by allocating tones for use in the CCM mode. Each

modem

51, 52 again measures the channel at each of the individual tones in the CCM portion of the tone. The method then proceeds to step s40, where in step s40 each modem estimates the number of bits that each such tone can support per frame (or per group of frames, since there should be some coding gain resulting from the spreading and despreading actions) in CCM mode based on the channel measurements employed in the previous steps.

The method then proceeds to step s50 where, in step s50, a chip-to-tone assignment is determined by the AN controller 1690 based on the estimated tone capacity. In this embodiment, this is trivial and may simply be performed on any arbitrary or convenient basis (e.g., numbering each generated chip to transmit in a single frame and assigning it to a similarly numbered tone), but in other embodiments this step may be important (e.g., employing frequency-spreading elements such that some chips encoding the same data are transmitted in the same frame, as discussed above with respect to the variations of the first embodiment).

Finally, at step s60, the system enters SHOWTIME, some data is transmitted over the portion of the tones allocated to the vectored DMT (which may include transmission according to the currently proposed method for transmitting downstream data according to the g.fast proposal/draft) and the rest is transmitted in CCM.

Turning now to fig. 5, a third embodiment of a CCM transmission system is shown, wherein, based on fig. 2, the same reference numerals have been used for the same components. Similar to fig. 2, this embodiment is intended to illustrate in principle an alternative CCM scheme in which FDMA is used instead of CDMA, and therefore this embodiment excludes details on how only a part of the tones can be used in CCM while the rest is used in vectored DMT mode (according to the second embodiment), details on upstream transmission, and so on. Although as with the other embodiments, it will of course be appreciated that actual embodiments will of course include such additional aspects, and that they have been omitted from fig. 5, and the discussion herein is merely for clarity and brevity. Fig. 5, while including

controllers

1691, 5191, and 5291 that function similarly to the controllers in fig. 3, has a slightly different function due to the FDMA nature of this embodiment. This functionality is described in more detail below with reference to fig. 6.

As can be seen from fig. 5, this third embodiment has a tone allocator 1680 in the AN1611 and

tone selector modules

5180, 5280 in the

modems

51, 52, instead of the spreader 1630 and

despreader

5130, 5230 modules. Also in FIG. 3, a second data source, data encoder, and S/P (DSDESP) module 1612 is illustrated as generating a data value d₁ ²To d_N ²Rather than d as is the case in fig. 2_M ². The reason for this is merely to emphasize that the same number of data values need not be generated by each of the two

DSDESP modules

1611, 1612 in this embodiment, as will become apparent. Accordingly, the output from the second M-QAM modulator 1622 is associated with the data value d passed thereto₁ ²To d_N ²A corresponding set of complex numbers x₁ ²To x_N ²。

In this embodiment, the M + N complex numbers generated by the first and

second modulators

1621 and 1622 are all passed to a tone allocator 1680, which allocates each of these values to a respective tone and then as complex values x'₁To x'_M+NForwarded (reordered otherwise unchanged) to the IFFT that receives all M + N values. In other words, there are M + N tones available and each of the complex values is assigned to a single respective tone. In particular, some tones are thus allocated to data from the first DSDESP module 1611, which is destined for the first modem 51, while the remaining tones are allocated to data from the second DSDESP module 1612, which is destined for the second modem 52. The complex numbers are then processed in a conventional manner by the IFFT and

AFE modules

1640, 1650, and the resulting signals are coupled to the two

TMPs

21, 22 via the coupler 2000, as in the first embodiment. At each

modem

51, 52, signals are received and processed as in the first embodiment to generate (after normal processing by the respective AFE, FFT and

FEQ modules

5150, 5250, 5140, 5240, 5160, 5260) a first modemValue y at 51₁ ¹To

And the value y at the second modem 52₁ ²To

These values should be very similar as in the first embodiment, but may be slightly different due to differences in the channel between AN16 and the first modem 51 and the channel between AN16 and the second modem 52. At each

modem

51, 52, these values y₁ ¹To

And y₁ ²To

And then passed to the respective

tone selector modules

5180, 5280, which (under the control of their respective controllers 5191, 5291) select only the values from the tones allocated to the modems, with which values a part is formed and as values

To

(for the first modem 51),

To

To its respective M-QAM demodulator 5120, 52020 (for the second modem 52) for demodulation. Each modem recovers only data destined for itself from all of the received data by selecting the correct value corresponding to the tone assigned to it only.

One important point to note is that (as described earlier in this application), since the channels (from each respective modem perspective) may be slightly different, it is possible that a particular tone may appear to be able to support more bits from a modem-by-modem perspective. In order to maximize the spectral efficiency of the overall transmission system, it is advantageous to allocate such tones to a modem that can receive a larger number of bits from a particular tone than another modem. And maximizing spectral efficiency, which also helps reduce the risk that data for one modem is being received and eavesdropped by another modem. However, this risk still exists, and all of the CCM methods described in this specification, where there is a security concern that data for one modem is intercepted by another encryption technique, should be employed to reduce this risk.

As the reader at this stage understands, the main function of the

controllers

1691, 5191 and 5291 is to both decide on the proper allocation of tones to the modems and to agree between them so that the transmitted data is correctly allocated to the intended tones and then to recover the correct data again at the receiving modem. To perform this function, the method illustrated in fig. 6 is performed. Note that the method described below with reference to fig. 6 assumes that there are devices that communicate between the controllers. This may be done in any convenient manner, including by means of the apparatus described above with reference to figures 3 and 4, or by any other suitable means.

Thus, referring now to fig. 6, at the beginning of the method at s10, AN16 transmits training signals over all tones and these signals are detected and measured by

modems

51, 52. Based on these measurements at the modems, each modem determines tone capacity (e.g., the number of bits the modem considers to be carried by a given tone per frame) and communicates it to AN controller 1691 at step s 20.

The method then proceeds to step s30 where the AN controller uses the assessment of each modem's capacity for each tone to determine AN intelligent allocation of tones to each

modem

51, 52 in step s30 in a manner to attempt to maximize the spectral efficiency of the system by allocating tones to the modems for which the maximum number of bits can be supported by those tones. An exemplary algorithm to achieve this is set forth in more detail below. Having determined the appropriate allocation in this manner, AN controller 1691 then notifies each modem controller 5191, 5521 which tones have been allocated to it (or more precisely to its modems 51, 52).

The method then proceeds to step s40, where in step s40 the actual data is sent from the AN16 to each of the modems in the FDMACCM mode of operation. In a preferred embodiment, the channel may be continuously measured and reported to AN controller 1691, which 1691 may periodically determine that the allocation of tones should be changed and then coordinate the allocation changes with the modem controller to continually optimize the transmission system despite changes in the noise environment.

Example Algorithm for allocating tones to modems

Any algorithm that generates a reasonably efficient tone allocation to the modem based on the number of bits that the modem can support in view of the tones may be used. As an example of just one such algorithm, the following pseudo code is given below:

if we will change the variable BPF_rDefined as the number of bits per frame received by the receiver r and variable BPT_t ^rDefined as the number of bits that a tone t can support for a receiver r, and if a tone t is allocated to a receiver r,_r,ttaking a value of 1, otherwise taking a value of 0, we specify that the algorithm seeks to have min { BPF } and Σ BPF for all receivers R (i.e., where 1 ≦ R ≦ R, where R is the total number of receivers (or end-user modems))_rBoth are maximized (summed over all receivers).

Setting T to the total number of tones;

setting R as the total number of receivers;

creating an integer array BPF [ R ] with all zero-valued elements;

creating a two-dimensional integer array BPT [ R, T ] with all zero-valued elements;

creating a two-dimensional binary array KDEL [ T, R ] having all zero-valued elements;

creating a one-dimensional Boolean array ALLOCATED [ T ] with all FALSE elements;

creating temporary integer variables rSEL and tSEL;

setting BPT r, t for each r and each t based on information provided from each receiver controller to the central controller (step s20 in fig. 6);

starting circulation;

selecting all r with BPF [ r ] as the minimum value (compared to the value of all BPF [ r ] for all r's values);

for all selected r and all not yet ALLOCATED tones t (where ALLOCATED t is FALSE),

setting rSEL r and tSEL t for which BPT r, t is maximum (if more than one is selected by any arbitrary process, e.g., the lowest value of t and/or the lowest value of r)

Set KDEL [ tSEL, rSEL ] to 1, ALLOCATED [ t ] to TRUE and

BPF[r]＝BPF[r]+BPT[rSEL,tSEL]；

for all r ≠ rSEL, set BPT [ r, tSEL ] to 0;

the loop is repeated until all t, ALLOCATED [ t ] ═ TRUE.

Briefly, the above algorithm iteratively identifies a receiver (or receivers) with the lowest (current) bits per frame, and identifies and assigns to it or them a number of tones (or one of the tones) that can support the highest number of bits for that receiver to the respective receiver, and then updates the number of bits per frame associated with that receiver and re-iterates.

Claims

1. A method of transmitting data from a transmitter device to a plurality of receiver devices, each of the plurality of receiver devices being connected to the transmitter device via a respective line connection, the method comprising the steps of:

transmitting a common signal to all or both of the respective line connections; and

using a multiple access technique enables the generation of respective virtual data channels for transmitting data from the transmitter device to each of the receiver devices via their respective virtual data channels,

wherein the common signals transmitted to all or both of the respective line connections are employed in a predetermined upper portion of an available spectrum available for communication over a metal wire pair connection, and in a lower portion of the available spectrum vectored discrete multi-tone transmission is used.

2. The method of claim 1, wherein the common signal is a discrete multi-tone signal in which a modulation level of each tone may be varied.

3. The method of claim 2, wherein the virtual data channel is formed using a code division multiple access technique.

4. The method of claim 2, wherein the virtual data channel is formed using a frequency division multiple access technique.

5. A method according to claim 3 or claim 4, wherein different modulation levels are used for data transmitted within the common signal within a given tone to different receiver devices, according to differences in received signal to noise ratios of signals received at the different receiver devices for the given tone.

6. A transmitter for transmitting data to at least first and second receiver devices via respective first and second line connections directly connecting each respective receiver device to the transmitter device using a discrete multi-tone communication method employed at frequencies at which there is significant indirect coupling between the line connections, the transmitter device comprising: a data combiner to combine a first set of data to be transmitted to the first receiver and a second set of data to be transmitted to the second receiver into a single common discrete multi-tone signal; and a line driver for driving both the first line connection and the second line connection with the common discrete multi-tone signal,

wherein the transmitter is operable to transmit the common discrete multi-tone signal onto all or both of the respective line connections in a predetermined upper portion of an available frequency spectrum available for communication over a metal wire pair connection, and is further operable to transmit a different respective vectored signal over each respective line connection in a lower portion of the available frequency spectrum.

7. A receiver apparatus for receiving data sent to the receiver apparatus over a wire connection from a transmitter according to claim 6, the receiver apparatus comprising: a receiver for receiving the common discrete multi-tone signal; and a data extractor for extracting from the common discrete multi-tone signal a first set of data transmitted by the transmitter for reception at the receiver device.

8. The receiver device of claim 7, wherein the data extractor comprises a despreader module for performing despreading operations on the received signal in accordance with a code division multiple access technique.

9. The receiver device of claim 7, wherein the data extractor comprises a tone selector to select a subset of values detected by the receiver and associated with different tones based on a predetermined allocation of tones of the receiver specified by the transmitter.